Polyimide copolymer and metal laminate using the same

ABSTRACT

Novel polyimide copolymer, which is a copolymer of isopropylidene-bis-(4-phenyleneoxy-4-phthalic acid)dianhydride and 6-amino-2-(p-aminophenyl)benzimidazole or a copolymer of two kinds of tetracarboxylic acid dianhydrides consisting of isopropylidene-bis-(4-phenyleneoxy-4-phthalic acid)dianhydride and 3,3′,4,4′-benxophenonetetracarboxylic acid dianhydride and 6-amino-2-(p-aminophenyl)benzimidazole, can form a metal laminate by direct lamination with metallic foils. The metal laminate can fully satisfy the peel strength.

TECHNICAL FIELD

The present invention relates to a novel polyimide copolymer and a metallaminate using the same and more particularly to a novel polyimidecopolymer effective for use preferably in bonding with metallic foilsand a metal laminate using the same.

BACKGROUND ART

Heretofore, metal laminates such as flexible wiring boards, etc. havebeen prepared by bonding metallic foils such as copper foils, etc. toaromatic polyimide films, using an adhesive of epoxy resin, urethaneresin, etc. However, flexible wiring boards prepared by using such anadhesive have suffered from various problems due to the adhesive used,such as peeling of the adhesive layer due to high temperatures in thesoldering step or use in high temperature circumstances, smeargeneration in the drilling step, etc.

To overcome such problems, it would be better to conduct directlamination of aromatic polyimide and metallic foils without use of theadhesive layer, but the peel strength of the most of the resulting metallaminates has not been satisfied yet.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an aromatic polyimidecapable of forming a metal laminate by direct lamination with metallicfoils and fully satisfy the peel strength of metal laminates thusformed.

Such an object of the present invention can be attained by a novelpolyimide, which is a copolymer ofisopropylidene-bis-(4-phenyleneoxy-4-phthalic acid)dianhydride and6-amino-2-(p-aminophenyl)benzimidazole or a copolymer of two kinds oftetracarboxylic acid dianhydrides consisting ofisopropylidene-bis-(4-phenyleneoxy-4-phthalic acid)dianhydride and3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride and6-amino2-(p-aminophenyl)benzimidazole.

For the tetracarboxylic acid dianhydrides of the present novel polyimidecopolymers, isopropylidene-bis(4-henyleneoxy4-phthalic acid)dianhydride:

or a mixture thereof with 3,3′,4,4′-benzophenonetetracarboxylic aciddianhydride:

can be used

When component (A) and component (B) are used together, component (B) isused m a proportion of not more than about 90 mol. %, preferably notmore than about 80 mol. % to tie mixture thereof with component (A).When component (B) is used in a higher proportion, the proportion ofcomponent (A) will be correspondingly not more than about 10 mol. %, andthe solubility of the resulting polyimide copolymer in an organicsolvent will be lowered

For diamine that reacts with these tetracarboxylic acid dianhydrides,6-amino-2-(p-aminophenyl)benzidazole can be used.

Reaction of tetracarboxylic acid dianhydride with diamine is carried outeven in an aprotic polar solvent such as dimethylformamide,dimethylacetamide, N-methyl-2-pyrrolidone, etc., but preferably in apolar solvent such as m-cresol, etc. Practically, a solution of diaminein a polar solvent is dropwise added to a solution of tetracarboxylicacid dianhydride in a polar solvent with stirring while keeping atemperature at about 0°-about 60° C., and after the dropwise additionreaction is carried out with stirring at a temperature of about 0°-about60° C. for about 0.5-about 5 hours. It seems that polyamic acid isformed by the reaction. To complete polyimidization reaction bydehydrating cyclization reaction, heating to about 100°-about 250° C.,preferably about 150°-about 200° C., is carried out with stirring forabout 2-about 8 hours in the latter half stage of reaction. A catalystsuch as benzoic acid, etc. is added to the solution of tetracarboxylicacid dianhydride and used for the reaction.

The reaction m is poured into an insoluble organic solvent such asmethanol, etc. to obtain white polyimide copolymer The resultingcopolymer has a glass transition temperature (Tg) of about 250°-about330° C. and η_(red) (N-methyl-2-pyrrolidone) of about 0.2-about 3.0 dl.When the copolymer is applied to lamination of metallic foils, thereaction mixture in a solution state can be directly applied tolamination of metallic foils without such separation of polyimidecopolymer from the solution of polyimide copolymer as the reactionmixture.

By reaction of tetracarboxylic acid dianhydride (A) with diane (C), apolyimide copolymer with the following repeat units can be obtained:

When tetracarboxylic acid dianhydride (A) is used together with (B), apolyimide copolymer with the following repeat units in addition to theabove-mentioned repeat units can be obtained by reaction with diamine(C):

Preparation of metal laminate using such a novel polyimide copolymer canbe carried out by applying a solution of polyimide copolymer to ametallic foil, typically a copper foil by casting, etc., followed byheating in two stages, ie. a temperature of about 60°-about 200° C.,preferably about 80°-120° C., and another temperature of about:150°-about 200° C., each for about 5-about 60 minutes, thereby forming apolyimide copolymer layer having a film thickness of about 3-about 75μm, i.e. forming a metal laminate with the metallic foil at one side ofthe copolymer layer. Another metallic foil is laid on the other side ofthe copolymer layer, followed by passing through and between laminaterolls heated to a temperature of about 150°-about 400° C., preferablyabout 200°-350° C. with processing, thereby easily bonding the metallicfoil directed specially to the transfer to the copolymer layer, i.e.forming a two-side laminate such as copper-lined material etc.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described below, referring to Examples.

EXAMPLE 1

A solution containing 26 g (0.05 moles) ofisopropylidene-bis-(4-phenyleneoxy-4-phthalic acid)dianhydride, 16.1 g(0.05 moles) of 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydrideand 12.2 g of benzoic acid dissolved in 500 ml of m-cresol was chargedinto a 4-necked flask having a capacity of 1 liter and a stirrer, and22.4 g (0.1 mole) of 6-amino-2-p-aminophenyl)benzimidazole was addedthereto while keeping a temperature at not more than 30° C., followed bysting at room temperature for one hour, thereby obtaining a polyamicacid solution. The solution as such was heated up to 200° C. andstirring was continued at that temperature for 5 hours. The reactionmixture was poured into 500 ml of methanol and the precipitates wererecovered by filtering and dried, whereby 61 g of polyimide copolymerwas obtained.

The polyimide copolymer thus obtained had Tg=308° C. and η_(red)(N-methyl-2-pyrrolidone)=1.20 dl and was soluble in dimethylformamide,dimethylacetamide, N-methyl-2-pyrrolidone and m-cresol.

A 15 wt. % solution of the polyimide copolymer in N-methyl-2-pyrrolidonewas applied to a copper foil (thickness: 18 μm) by casting, and theapplication layer was heated at 80° C. for 30 minutes and then at 180°C. for 30 minutes to form a lamination sheet having a thickness of 25 μmon the copper foil By aging at 260° C. for 2 hours, a one-side laminatewith no curling was obtained. Then, another copper foil (thickness: 18μm) was laid on the other side of the lamination sheet, followed bypassing through and between laminate rolls heated to 330° C. whilepressing, thereby conducting pressure bonding to obtain a two-sidelaminate.

The resulting laminate of copper foil/polyimide copolymer/copper foilwas subjected to determination of peel strength according to JIS C-6481,and found to be 2.1 kg/cm under room temperature conditions and 1.4kg/cm under heating conditions of 150° C. Furthermore, when solderingheat resistance thereof was observed under conditions of 300° C. for oneminute, no swelling of polyimide copolymer layer was found.

EXAMPLE 2

In Example 1, no 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydridewas used, while the amount ofisopropylidene-bis-(4phenyleneoxy-4phthalic acid)dianhydride was changedto 52 g (0.1 mole). 71 g of polyimide copolymer was obtained.

The resulting polyimide copolymer had Tg=275° C. and η_(red)(N-methyl-2-pyrrolidone)=1.20 dl and was soluble in dimethylformamide,dimethylacetamide, N-methyl-2-pyrrolidone, phenol and m-cresol.

A laminate of copper foil (18 μm)/polyimide copolymer (25 μm)/copperfoil (18 μm) was prepared, using a 15 wt. % solution of the polyimidecopolymer in N-methyl-2-pyrrolidone in the same manner as in Example 1,and the peel strength of the laminate was determined and found to be 1.8kg/cm under room temperature conditions and 1.6 kg/cm under heatingconditions of 300° C. for one hour. No swelling was found in thesoldering heat resistance test.

COMPARATIVE EXAMPLE

In Example 1, no isopropylidene-bis-(4phenyleneoxy-4phthalic acid)dianhydride was used, but the amount of3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride was changed to32.2 g (1.0 mole). 50 g of polyimide copolymer was obtained.

The resulting polyimide copolymer had Tg=390° C. and was insoluble indimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone andm-cresol That is, neither solution nor laminate with copper foils couldbe formed.

INDUSTRIAL APPLICABILITY

The present novel polyimide copolymer per se has a high bonding strengthand can give a metal laminate satisfying the peel strength even ifbonded to a metallic foil without any adhesive layer as an intermediate.Furthermore, the distinguished soldering heat resistance enables themetal laminate to serve as a flexible metal foil-lined laminate board insuitable use for flexible wiring board, etc. without curling.

What is claimed is:
 1. A novel polyimide copolymer, which comprises acopolymer of isopropylidene-bis-(4-phenyleneoxy4-phthahicacid)dianhydide and 6-amino-2-(p-aminophenyl)benzimidazole.
 2. A novelpolyimide copolymer, which comprises a copolymer of two kinds oftetracarboxylic add dianhydrides consisting ofisopropylidene-bis-(4-phenyleneoxy-4-phthalic acid)dianhydride and3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride, and6-amino-2-p-aminophenyl)benzimidazole.
 3. A process for preparing anovel polyimide copolymer, which comprises reactingisoproylidene-bis-(4phenyleneoxy-4phthalic acid)dianhydride or two kindsof tetracarboxylic add dianhydrides consisting of isopropylidenebis-(4-phenyleneoxy-4-phthalic acid)dianhydride and3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride, with6-amino-2-(p-aminophenyl)-benzimidazole in a polar solvent, therebyforming a polyamic acid, followed by conducting dehydrating cyclizationreaction.
 4. A process for preparing a novel polyimide copolymeraccording to claim 3, wherein the polar solvent is m-cresol.
 5. Aprocess for preparing a novel polyimide copolymer according to claim 3,wherein the reaction is carried out in the presence of a benzoic acidcatalyst.
 6. A novel polyimide copolymer according to claim 1 for usebonding to a metallic foil.
 7. A novel polyimide copolymer according toclaim 2 for use in bonding to a metallic foil.
 8. A metal laminate witha metallic foil laid on one side of a layer of polyimide copolymeraccording to claim
 1. 9. A metal laminate with a metallic foil laid onone side of a layer of polyimide copolymer according to claim
 2. 10. Ametal laminate with metallic foils laid on both sides of a layer ofpolyimide copolymer according to claim 1, respectively.
 11. A metallaminate with metallic foils laid on both sides of a layer of polyimidecopolymer according to claim 2, respectively.